In some content protection systems, a media device (e.g., a Blu-ray Disc) provides a host player (e.g., a Blu-ray Disc player) with encrypted digital content (e.g., a high-definition movie) for decryption and playback. The content contains many sets of duplicate video frames that are nearly identical to one another but have some slight variation. There are many alternate navigation paths through these duplicate frames, and the host player selects a particular navigation path based on the device key of the group it belongs to within the key tree structure of the Media Key Block of the host player. Accordingly, the specific ones of the duplicate frames rendered by the host player provide a unique signature (or “watermark”) from which to identify the host player. In this way, if a content title were to be pirated, the pirated copy can be analyzed to determine the navigation path that was used and, thus, the identity of the particular host player that generated the pirated copy. Once the compromised host player is identified, the host player's certificate and key can be revoked, so that the host player will no longer be able to decrypt (and possibly pirate) further content, thereby containing the potential revenue loss of the content provider due to the host player's security breach. For example, new certificate revocation lists can be distributed with future releases of content, so that the compromised host player will be disabled when it attempts to play a new content title. However, the effectiveness of the solution is measured by the number of recovered content it takes to precisely detect the compromised host player in the ecosystem. This leads to a delay in detecting the compromised host player and also contains a probabilistic detection of the absolute guilty device.
These content protection systems can face a “fox guarding the hen house” problem in that the entity responsible for injecting the watermark into the content is the compromised host player itself. Accordingly, there is a concern that once the host player is compromised to allow content to be pirated, it may be further compromised to remove the watermark injection functionality.